Electric resistance wire and spring wire is frequently formed into permanently set coils formed by winding the wire on a mandrel having the cross-sectional shape and dimension of the desired coil configuration.
To produce a permanently set coil, the wire is usually wound on a mandrel under back-tension, the mandrel having a cross-sectional size related to the diameter of the wire and the wire's elastic limit so that as the wire bends on the mandrel its elastic limit is exceeded so that the wire becomes permanently deformed.
One way for doing this is to use a long rotating mandrel requiring both of its ends to be rotatively supported, the wire being fed to one end of this mandrel from a supply spool which is moved along the length of the mandrel so that the wire is progressively wound on the mandrel and a coil length is produced. Then one end of the mandrel must be freed so this coil can be removed from the mandrel. This practice is objectionable because it is a discontinuous operation and the coil length can be no longer than that of the mandrel.
For continuous coil production, the rotating mandrel can be made very short and have a free front end with its back end forming a conical flange, rotating with the mandrel, to which the wire is fed from a stationary supply spool, pressure rolls rotating about axes parallel to the mandrel pressing a few of the convolutions of the forming coil against the mandrel to obtain a friction drive overcoming the back-tension on the wire feed. The wire running against the conical flange wedges itself between this rotating flange and the wire just previously coiled so as to force the coil continuously from the free end of the mandrel, producing a continuous production of wire coil. A major objection to this practice is that the continuously produced coil is a rotating coil which after reaching a critical length begins to thrash about and become unmanageable, this requiring continuous cutting of the coil into lesser lengths possibly no greater than that obtainable from the long mandrel practice described above.
To overcome the above objection, the short mandrel can be non-rotating and the supply spool revolved about the mandrel so as to wind the wire on the mandrel starting at the mandrel's back end. However, in this case there is no rotating conical flange that can be used for coil feeding as described above and, therefore, complicated screw-type guides, cams rotating in synchronism with the revolving supply spool, and other mechanical parts have been required. An example of this practice is provided by the Moebus U.S. Pat. No. 3,503,236, May 31, 1970. Such mechanical complications are commercially objectionable.